чем определен угол роста растений ауксин зависимый рост

Please cite this article in press as: Roychoudhry et al., Auxin Controls Gravitropic Setpoint Angle in Higher Plant Lateral Branches,Current Biology (2013), http://dx.doi.org/10.1016/j.cub.2013.06.034

Auxin Controls Gravitropic S

Current Biology 23, 1–8, August 5, 2013 ª2013 The Authors http://dx.doi.org/10.1016/j.cub.2013.06.034

Reportetpoint

Angle in Higher Plant Lateral Branches

Suruchi Roychoudhry,1 Marta Del Bianco,1,2 Martin Kieffer,1

and Stefan Kepinski1,*1Centre for Plant Sciences, University of Leeds, Leeds, LS29JT, UK

Summary

Lateral branches in higher plants are often maintained atspecific angles with respect to gravity, a quantity known as

the gravitropic setpoint angle (GSA) [1]. Despite the impor-tance of GSA control as a fundamental determinant of plant

form, the mechanisms underlying gravity-dependent angledgrowth are not known. Here we address the central ques-

tions of how stable isotropic growth of a branch at a nonvert-

ical angle is maintained and of how the value of that angle isset. We show that nonvertical lateral root and shoot

branches are distinguished from the primary axis by theexistence of an auxin-dependent antigravitropic offset

mechanism that operates in tension with gravitropicresponse to generate angled isotropic growth. Further, we

show that the GSA of lateral roots and shoots is dependentupon themagnitude of the antigravitropic offset component.

Finally, we show that auxin specifies GSA values dynami-cally throughout development by regulating the magnitude

of the antigravitropic offset component via TIR1/AFB-Aux/IAA-ARF-dependent auxin signaling within the gravity-

sensing cells of the root and shoot. The involvement of auxinin controlling GSA is yet another example of auxin’s remark-

able capacity to self-organize in development [2] andprovides a conceptual framework for understanding the

specification of GSA throughout nature.

Results and Discussion

Primary and Lateral Shoots Are Distinguished by theExistence of an Angle Offset Mechanism

To begin to analyze the mechanism that generates gravity-dependent nonvertical growth, we performed decapitationexperiments in Arabidopsis thaliana (Arabidopsis) and Pisumsativum (pea) shoots. The removal of the primary shoot apicalmeristem (SAM) in many species results in the branch of thesubapical node becoming the new main shoot apex [3]. Weobserved that this assumption of a leading, primary role isaccompanied by a shift to a near vertical gravitropic setpointangle (GSA) in the subapical branch, a transition occurringover the course of 48 to 72 hr (Figure 1B). This change inGSA is suppressed by the application of auxin (1 mM indole-3-acetic acid [IAA] in lanolin) to the apical stump (Figures 1Band 1C), indicating the existence of a developmental switchthat shares features with the mechanism regulating bud

2Present address: Dipartimento di Biologia e Biotecnologie, Universita di

Roma, Sapienza, Via dei Sardi, 70-00185 Rome, Italy

*Correspondence: [email protected]

This is an open-access article distributed under the terms of the Creative

Commons Attribution License, which permits unrestricted use, distribution,

and reproduction in any medium, provided the original author and source

are credited.

outgrowth [3]. These data demonstrate that the GSA of non-vertical lateral branches and the approximately vertical pri-mary axis is determined principally on the existence of, orlack of, some kind of angle offset mechanism.

Stable Nonvertical Growth of Shoot and Root Branches Is

Sustained by an Antigravitropic Offset MechanismUpon being displaced either above or below its GSA, an organwill rapidly undergo a gravitropic response to return to its orig-inal angle of growth [1,4] (Figures S1A–S1D and the Supple-mental Introduction available online). For lateral root and shootbranches, this requires reorientation both with and against thegravity vector, demonstrating unequivocally that the mecha-nistic basis for the robust maintenance of nonvertical growthcannot lie solely in differences in gravitropic competencebetween primary and lateral organs. At the same time, thefact that a lateral branch can switch to a vertical GSA statewhere the maintenance of growth angle is accounted for byCholodny-Went-based gravitropic response (reviewed in [5])suggests that parsimonious hypotheses for the nature of theangle offset mechanism should include Cholodny-Went grav-itropism as the means of reorientating lateral organs upondisplacement from their GSA. Thus there are two classes ofoffset mechanism to consider initially. In the first, perceptionof the orientation of the gravity vector is shifted such thatdespite a branch being inclined from the vertical, no asymme-try in auxin response is generated, while in the second, theperception of the gravity vector in the branch is the same asin the primary axis. Here, the anisotropic growth that wouldotherwise develop in response to radial asymmetry in auxinresponse must be counteracted by an opposing, antigravi-tropic anisotropy to generate net isotropic, nonvertical growth.To distinguish these two classes of mechanism, we used ahorizontal one-dimensional clinostat to subject shoots androots to omnilateral gravitational stimulation. We reasonedthat if nonvertical GSAs were the product of balancing gravi-tropic and antigravitropic components, then clinorotationmight reveal the effects of the latter. In these experiments,Ara-bidopsis plants were rotated horizontally at speeds from 4revolutions per hour (rph) to 1 revolution per minute (rpm).After 8 hr of clinorotation, we observe that cauline branchesgrow with a marked outward/downward anisotropy (assessedin relation to the vertical in upright plants) consistent with theaction of an antigravitropic growth component operating inthe absence of balancing gravitropic response (Figures 1Dand 1E). This effect was the same regardless of whether shootbranches were on or off the axis of rotation (Figures S1E andS1F). We observed a similar pattern of outward/upwardgrowth in Arabidopsis lateral roots subjected to clinorotation,again, either on or away from the axis of rotation, indicatingthat a common mechanism might underlie these similar rootand shoot responses (Figures 1G, 1H, S1E, and S1F).This idea of an antigravitropic growth component is a very

old one: de Vries in 1872, in some of the earliest clinorotationexperiments, noted a similar outward bending of lateral organsfrom several species, a phenomenon he named epinasty [6].Subsequent researchers have confirmed these observationsin species including Coleus blumei Benth., wheat, pea, andCapsicum annuum, and remarkably, these so-called epinastic

http://dx.doi.org/10.1016/j.cub.2013.06.034


mailto:[email protected]

A B C

D E F

G H I

Figure 1. The Nonvertical GSA of Lateral Shoots and Roots Is Driven by a Lateral Branch-Specific Auxin-Dependent Antigravitropic Offset Mechanism

(A) Typical GSA profiles of A. thaliana (Col. 0) shoot and root branches with diagram of GSA designations.

(B and C) Changes in the GSA of Arabidopsis and pea subapical branches after removal of the shoot apex and application of 1mM IAA or mock treatment to

the apical stump (white arrowheads, decapitated apices; red arrowheads, subapical lateral branches) (B). Quantitative analysis of branch GSA is shown (p <

0.05; error bars indicate the SEM) (C).

(D, E, G, and H) Effect of horizontal clinorotation on lateral shoot (D and E) and lateral root (G and H) GSA. Note: for clinorotated plants, a nominal GSA was

derived by measurement of the growth angle of the final 5 mm of cauline branches and 2 mm of lateral roots with respect to the vertical in upright plants.

Green and red lines represent the action of gravitropic and antigravitropic growth components, respectively. Lateral shoot GSA (E) and lateral root GSA (H) in

wild-type and ein2-1 mutant plants are shown.

(F and I) Effect of local application of the auxin transport inhibitor NPA and subsequent clinorotation on lateral shoot (F) and lateral root GSA (I).

Clinorotation at 4 rph (D–F) and 1 rpm (G–I). Scale bars represent 1 cm (D) and 0.5 cm (G). Error bars indicate the SEM. See also Figure S1.

Current Biology Vol 23 No 152


phenomena have also been observed in early space flight-based experiments in the late 1960s [7–11]. The nature of thesegrowth responses in lateral organs has, however, been the

subject of forceful debate with arguments advanced that theobserved outward anisotropy is merely an ethylene-mediatedstress response to clinorotation rather than an effect of the

Auxin Controls Plant Gravitropic Setpoint Angle3


withdrawal of normal gravitational stimulation [10–14]. Toaddress this crucial question, we performed clinorotationexperiments with the Arabidopsis mutant ein2-1, which iscompletely insensitive to ethylene ([15] and data not shown).Horizontal clinorotation of ein2-1 induces outward anisotropicgrowth of cauline branches and lateral roots as observed inwild-type Col-0, confirming that these patterns of branchgrowth are not ethylene-mediated responses to physicalmovement while horizontal (Figures 1E, 1H, S1H, and S1I).We performed several additional experiments to ensure thatthe patterns of branch growth observed on the clinostat reflectthe underlying biology of GSA control rather than artifacts ofclinorotation (Figures S1E–S1G and the accompanyinglegend). Together, these data are not consistent with a modelfor the maintenance of nonvertical lateral branch GSAs basedon an altered gravity perception, which we predict wouldrespond to omnilateral gravitational stimulation with isotropicgrowth as in the primary shoot and root (data not shown).Rather, they support the idea that standard Cholodny-Wentgravitropic response, which would otherwise cause bendingto the vertical, is balanced by an antigravitropic offsetcomponent.

The Antigravitropic Offset Mechanism Is Auxin DependentTo test whether or not auxin transport is required for the actionof the antigravitropic offset, we performed clinorotation exper-iments in the presence of the auxin transport inhibitor NPA. Forshoot experiments, NPA or mock treatments were applied tobranches via a thin layer of lanolin. Cauline branches treatedwith 10 mMNPA in this manner 2 hr before clinorotation displaya significant reduction in outward anisotropic growth (Fig-ure 1F). For root system experiments, plants were grown onmedia containing 0.2 mMor 1 mMNPA, representing treatmentswhere the gravitropism of primary and lateral roots is eithermildly (0.2 mM) or more severely (1 mM) affected ([16, 17] anddata not shown). Both of these NPA treatments are sufficientto dramatically reduce outward/upward bending in clinoro-tated lateral roots, indicating that auxin transport is alsorequired for the activity of the antigravitropic offset in theroot (Figure 1I).

These auxin transport experiments are consistent with clas-sical data on auxin distribution in clinorotated lateral organsderived from the Avena bioassay and the use of radiolabelledIAA [10, 18, 19]. Together, they suggest that the antigravitropicgrowth component that opposes gravitropic responses inlateral branches is also driven by auxin. The action of thesegravitropic and antigravitropic auxin components is illustratedin Figures 1D and 1G: under normal upright growth conditions,gravitropism (green line) that would otherwise move thebranch toward the vertical is counteracted by antigravitropism(red line), resulting in net symmetry in auxin response andhence isotropic but angled growth. Under clinorotation andin the absence of a stable gravity reference, auxin movementto the lower side of the shoot or root branch is lost whilecontinued antigravitropism sustains auxin levels on the upperside, driving outward anisotropic growth.

This model for the maintenance of gravity-dependent non-vertical growth retains the central element of the Cholodny-Went hypothesis in that isotropic growth at any given GSA isthe result of symmetrical auxin distribution and responsebetween opposite sides of an organ while asymmetry inresponse leads to anisotropic growth. Thus in a given nonvert-ical GSA state the antigravitropic offset can be thought of aslargely constant regardless of the actual orientation of the

branch. In contrast, the gravitropic component is continuouslyvariable according to branch orientation within the gravityfield. For a shoot branch that is shifted to amore vertical angle,an initial decrease in the magnitude of the gravitropic compo-nent would prompt outward/downward anisotropic growthdriven by the constant antigravitropic offset. This downwardbending would diminish as the magnitude of the gravitropiccomponent increased with the increasing displacement ofstatoliths as the branch moves back away from the vertical.For a shoot branch displaced to an angle less vertical thanits GSA, the reverse would apply, with an increasedmagnitudeof gravitropic response consistent with the general principlesof sine law (see the Supplemental Introduction) [20, 21].This mechanistic model for the maintenance of nonvertical

growth predicts that lateral branches with the least verticalGSA should display the greatest abaxial bending upon clinor-otation. We tested this idea by recording the response oflateral roots and cauline branches of different lengths to thewithdrawal of a stable gravity reference; both lateral rootsand cauline branches emerge at very shallow GSAs, becomingincreasingly vertical as they grow longer (Figures 1A and S1A–S1D). Consistent with this manifest relationship betweenbranch length and GSA, we observed that the shortest rootand shoot branches exhibited the greatest degree of curvatureupon clinorotation and the longest branches the least (Figures2A and 2B). These data indicate that the GSA of a given organis determined by the magnitude of its antigravitropic offset(which may be a zero or nonzero value) and provide confirma-tion that the model for GSA maintenance presented here canaccount for the observed GSA biology of lateral root and shootbranches.

Auxin Specifies theMagnitude of the Antigravitropic Offset

and Hence the GSA of Lateral Shoots and RootsIn exploring the involvement of auxin in regulating the transi-tion nonzero to zero antigravitropic offset states in decapita-tion experiments, we also noticed that mutants with defectsin auxin homeostasis or response have altered lateral organGSA (Figure S2, summarized in Figure 2E). Mutants with higherlevels of auxin (yucca1-1D [22], yuc1D [23]) or a predictedhigher level of auxin response (axr3-10 [24], arf10-3 arf16-2[25], arf10-3 arf16-2 axr3-10), have lateral shoots or rootsthat are more vertical than wild-type. In contrast, mutantswith lower levels of auxin (wei8 tar2 [23]) or auxin response(the auxin receptor mutants tir1-1 [26], afb4-2 afb5-5 [27])have lateral branches that are less vertical (Figures 2D andS2A–S2D). We confirmed that these changes in root and shootbranch growth angle were bona fide GSA phenotypes by per-forming reorientation assays with tir1-1, axr3-10, and arf10-3arf16-1 (Figures S3A and S3B). Consistent with all of thesegenetic data, lateral roots cultured on media containing IAAand 2,4-dichlorophenoxyacetic acid (2,4-D) in the nanomolarrange grow at increasingly vertical GSA values (Figures 2Cand S2F). We observed a similar effect of auxin on lateralroot GSA in bean (Phaseolus vulgaris) and rice (Figure S2H).Only one set of mutants ran counter to this simple relation-

ship between auxin response and GSA phenotype; NPH4/ARF7 and ARF19 are from the subclade of auxin response fac-tors (ARFs) that have been characterized as transcriptionalactivators [27]. Cauline branches of nph4-1 arf19-1 [28] areconsiderably less vertical than the wild-type (Figures 2D, 2E,and S2G). After decapitation, the subapical branch in nph4-1arf19-1 undergoes the same shift toward the vertical observedin wild-type, suggesting that the GSA phenotype in this mutant

A B C

D E

Figure 2. Auxin Regulates Shoot Branch and Lateral Root GSA

(A and B) Magnitude of outward anisotropic growth in cauline branches (A) and lateral roots (B) of increasing ages (defined as branches length size classes)

after 8 hr of clinorotation, 4 rph (A) and 1 rpm (B).

(C) Effect of auxin (IAA, 2,4-D) onwild-type (Col-0) lateral root GSA; changes in GSA asmeasured along lateral roots in successive 0.8mmsegments (mean of

12–15 lateral roots, one-way ANOVA, p < 0.05 for data points 4–10).

(D) Typical GSA profiles of lateral shoots and roots of wild-type and auxin signaling mutants (tir1-1, nph4-1 arf19-1, arf10-3 arf16-2 axr3-10) with or without

IAA treatment.

(E) Schematic representation of the effect of auxin synthesis and signaling mutants on lateral shoot and root GSA (data presented in Figures S3 and S4).

Black lines represent the primary axis and lateral branches, black arrows changes in branch GSA and red arrows higher and lower levels of auxin or auxin

response, respectively.

Scale bars represent 1 cm (D, top) and 0.5 cm (D, bottom). Error bars indicate the SEM. See also Figure S2.



represents a bona fide defect in GSA control rather than one ingravitropic response (Figure S2I). In the root, loss of NPH4/ARF7 function has the opposite effect with arf7-201 [29] lateralroots growing at a more vertical GSA (Figure S2J). For exami-nation of the effects of the combined loss of ARF7 and ARF19function on lateral root GSA, it was necessary to perform theanalysis on media containing auxin in order to induce lateralroot formation. Under these conditions, nph4-1 arf19-1 lateralroots have a GSA that is significantly more vertical than that ofwild-type plants grown at the same concentration of IAA (Fig-ures 2D, 2E, and S2K).

Thus, with the exception of NPH4/ARF7 and ARF19, theremoval of negative regulators of auxin signaling (e.g., repres-sing ARFs and Aux/IAAs) causes lateral branch GSA to bemore vertical, while the removal of positive regulators of auxinsignaling (e.g., TIR1) induces a less vertical phenotype. Inaddition to any alterations in basic gravitropic response inthese mutants, these data indicate that TIR1 is a negative

regulator of the antigravitropic offset, while ARF10, ARF16,and AXR3 are positive regulators of this mechanism.To test this hypothesis, we performed clinorotation experi-

ments with mutants or treatments that induce more or lessvertical lateral GSA phenotypes. In both the shoot and root,mutants with a less vertical GSA (tir1-1 in both root and shoot,nph4-1 arf19-1 in the shoot only) exhibit a greater degree ofoutward anisotropy, while those with a more vertical GSA(arf10-3 arf16-2 in the shoot, axr3-10 and auxin treatment inthe root) exhibit less bending (Figures 3, S3C, and S3D). Weconclude that auxin acts to alter the GSA of a lateral organby changing the magnitude of the antigravitropic offset.

The Auxin-Mediated Specification of Shoot Branch GSA Is

Effected in the Gravity-Sensing Cells of the Shoot and theRoot

To identify the cell types in which changes in auxinsensitivity can affect GSA, we altered auxin signaling in a

A C

B D

Figure 3. Auxin Regulates GSA by Modulating the

Magnitude of the Antigravitropic Offset

Changes in lateral shoot GSA (A and C) and lateral

root GSA (B and D) after clinorotation (4 rph and 1

rpm, respectively, 8 hr) in wild-type and auxin

response mutants and auxin-treated seedlings.

Shoot branch GSA, tir1-1 (A and C), nph4-1

arf19-1 and arf10-3 arf16-2 (C); lateral root GSA,

tir1-1, 50 nM 2,4-D (B and D) axr3-10 with corre-

sponding wild-type controls (D).

(A andB) Control untreated plants (top panels) and

a clinorotated plants (bottom panels).

(C and D) Graphs comparing the magnitude of

bending (degrees of curvature) in different auxin

response mutants, and in response to 2,4-D treat-

ment, upon clinorotation (p < 0.05, one-way

ANOVA, n = 15–20).

Scale bars represent 1 cm (A) and 0.5 cm (B). Error

bars indicate the SEM. See also Figure S3.



cell-type-specific manner beginning with the gravity-sensingcells from which auxin fluxes associated with graviresponseare directed. In the shoot, these statocytes are located inendodermis, a tissue marked by the expression of theArabidopsis gene SCARECROW (SCR) [30]. Previous workon auxin signaling in embryogenesis included the character-ization of a transgenic line expressing the mutant stabilizedAux/IAA corepressor protein mutant bodenlos/iaa12 (bdl) un-der the control of the SCR promoter (SCR::bdl) [31]. Only onepostembryonic phenotype of SCR::bdl was described, thatof a defect in cauline branch gravitropism. We examined thisline and established that the defect is not a principally one ofgravitropism but rather a change in GSA control; the primaryinflorescence displays a normal vertical GSA, while the caulinebranches have an extreme nonvertical GSA (Figures 4A and4C). We demonstrated that this was a bona fide defect inGSA control by confirming that upon decapitation of the pri-mary SAM, subapical cauline branches in SCR::bdl transitionfrom an extreme nonvertical GSA to a near vertical one, reflect-ing the loss of antigravitropic offset and confirming that thecauline branches retain gravitropic competence but have anparticularly strong antigravitropic offset (Figure 4A). To pro-vide additional evidence of the importance of variation in auxinsignaling in shoot statocytes for GSA control, we generatedArabidopsis plants expressing an inducible SCR::bdl:GR

construct. Dexamethasone treatment ofthese lines induces a less vertical GSAstate in shoot branches, again, withoutaffecting the GSA of the primary shoot(Figure S4). This induced GSA state,consistent with the activity of a strongantigravitropic offset, is lost 72 hr afterthe cessation of dexamethasone induc-tion (Figure S4B).There are strong similarities between

SCR::bdl and SCR::bdl:GR plants andnph4-1 arf19-1 mutants, all having theleast vertical shoot branch GSA pheno-types of the mutants tested here. bdl/iaa12 is a stabilizing gain-of-function mu-tation, and BDL/IAA12 protein has beenshown to interact with NPH4/ARF7 andARF19 [32]. Thus, regardless of the

contribution of wild-type BDL/IAA12 to GSA control, the likelybdl-mediated blocking of ARF action, including NPH4/ARF7and ARF19, in just the shoot endodermal statocytes is suffi-cient to modulate the GSA of shoot branches. To test theidea that variation in NPH4/ARF7-mediated signaling in shootstatocytes alone can alter the GSA of shoot branches, wemade transgenic plants expressing an inducible form ofARF7 in endodermal statocytes (SCR::ARF7:GR). Dexametha-sone treatment of these plants induces a very vertical caulinebranch GSA phenotype (Figures 4B and 4D), consistent withthe hypothesis that ARF7 is a negative regulator of the antigra-vitropic offset in the shoot and further, that changes in auxinresponse in the shoot statocytes alone are sufficient to specifyGSA values of shoot branches.To test whether the modulation of auxin sensitivity in the

gravity-sensing cells of the columella root cap is similarly suf-ficient to alter lateral root GSA, we used the GAL4 transactiva-tion system [33]. Plants expressing a stabilized version ofAux/IAA AXR3/IAA17 under the control of the UAS promoter(UAS::axr3-1) were crossed to the enhancer-trap lines J1092(driving GAL4 expression in the columella and lateral rootcap [LRC]) and M0013 (driving GAL4 expression in the LRC)[33]. Expression of the hypermorphic/neomorphic axr3-1mutant protein in the columella and LRC but not the LRCalone causes lateral roots to grow with a more vertical GSA

A

B C

E D

F G

Figure 4. Auxin specifies GSA within the gravity-sensing cells of the root and shoot

(A and C) Shoot GSA phenotypes of 28-day-old intact wild-type plants and intact and decapitated SCR::bdl plants.

(B and D) Shoot GSA phenotypes of 28-day-old mock- and Dex-treated SCR::ARF7:GR plants.

(C and D) Quantification of lateral shoot GSA in (intact) wild-type and SCR::bdl plants (C) and in mock- and Dex-treated SCR::ARF7:GR plants (D).

(E and F) Root GSA phenotypes of plants expressing stabilized axr3-1/iaa17 under the control of the UAS promoter (UAS::axr3-1) in the GAL4 driver line

backgrounds M0013 (expression in the lateral root cap [LRC]) and J1092 (expression in the LRC and columella). Quantification of lateral root GSA in

(legend continued on next page)





(Figures 4E and 4F). These data demonstrate that the modu-lation of auxin signaling specifically in the columella stato-cytes is sufficient to alter lateral root GSA without affectingprimary root GSA, indicating that, as in the shoot, it is withinthe statocytes that the auxin-dependent regulation of themagnitude of the antigravitropic offset and hence GSA iseffected.

ConclusionsThe data presented here have revealed four fundamental fea-tures of GSA control in Arabidopsis. First, the GSA states ofthe near-vertical primary axis and nonvertical lateral branchesare distinguished by the existence of an antigravitropic offsetmechanism operating in the latter. Second, the antigravitropicoffset mechanism is auxin dependent and acts in tension withgravitropism to generate net symmetry in auxin levels andresponse between the upper and lower sides of lateralbranches. Third, the GSA of graviresponsive organs is depen-dent on the magnitude of the antigravitropic offset and itsinteraction with gravitropic response. Fourth, auxin specifiesnonvertical GSA values by modulating the magnitude of theantigravitropic offset component within the gravity-sensingcells of lateral roots and shoots.

The principal features of this model of GSA control are illus-trated in Figure 4G, which depicts the basic relevant relation-ships between auxin, auxin transport, and auxin signalingwithin the gravity-sensing cells of the root and shoot. It isimportant to emphasize that there are two mechanisticallydistinct roles for auxin in this model: in addition to drivingisotropic growth itself in the epidermis, auxin and auxinsignaling within the gravity-sensing cells is negatively regu-lating the magnitude of the antigravitropic offset mechanism.The mechanisms we have identified also provide multiplenodes through which environmental signals relating toresource status (in particular nutrients below ground and lightabove) can be integrated such that changes to optimizeresource capture can be effected.

The dependence of the antigravitropic offset on auxin trans-port is consistent with the fact that changes in auxin signalingsolely within gravity-sensing cells is sufficient to bring aboutchanges in growth in nonadjacent epidermal tissues. In estab-lishing the molecular basis of the antagonistic interaction ofgravitropic and antigravitropic offset components, an obvioushypothesis to test will be whether this antagonism lies inopposing inputs into the polarity of PIN protein localizationor activity in gravity-sensing cells; PIN localization and activitydepend upon PIN protein phosphorylation [34, 35], and so itwill be interesting to examine the extent to which gravity-dependent, nonvertical growth might stem from competingphosphatase and kinase activities regulating the phosphoryla-tion state, and hence net symmetry of PINs or PIN activitywithin statocytes. The ability to separate gravitropic and anti-gravitropic offset components as described here provides apowerful experimental system to test this and other hypothe-ses. We predict that the general principles of GSA controlthat we have set out here will be of wide relevance throughoutthe higher plants and thus provide a conceptual framework forunderstanding GSA variation throughout nature.

wild-type and plants expressing axr3-1 under the control of the two driver line

(G) Schematic model of the action of the auxin-dependent gravitropic and ant

ated regulation of the antigravitropic offset by auxin that occurs within the grav

antigravitropic auxin transport components, respectively.

Scale bars represent 1 cm (A and B) and 0.5 cm (E). Error bars indicate the SE

Supplemental Information

Supplemental Information includes Supplemental Introduction, Supple-

mental Experimental Procedures, and four figures and can be found with

this article online at http://dx.doi.org/10.1016/j.cub.2013.06.034.

Acknowledgments

We are grateful to Ottoline Leyser for stimulating discussions and critical

reading of the manuscript. We also thank Dolf Weijers for sending seeds

and Mark Estelle, Przemysław Prusinkiewicz, and Jurgen Klein-Vehn for

comments on the manuscript. This work was funded by grants from the

EPSRC (EP/G039496/1) and BBSRC (BB/K010956/1).

Received: November 30, 2012

Revised: April 28, 2013

Accepted: June 13, 2013

Published: July 25, 2013

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Technology

чем определен угол роста растений ауксин зависимый рост